  /*
    2    * Copyright (c) 1995, 2000, Oracle and/or its affiliates. All rights reserved.
    3    * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
    4    *
    5    * This code is free software; you can redistribute it and/or modify it
    6    * under the terms of the GNU General Public License version 2 only, as
    7    * published by the Free Software Foundation.  Oracle designates this
    8    * particular file as subject to the "Classpath" exception as provided
    9    * by Oracle in the LICENSE file that accompanied this code.
   10    *
   11    * This code is distributed in the hope that it will be useful, but WITHOUT
   12    * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   13    * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   14    * version 2 for more details (a copy is included in the LICENSE file that
   15    * accompanied this code).
   16    *
   17    * You should have received a copy of the GNU General Public License version
   18    * 2 along with this work; if not, write to the Free Software Foundation,
   19    * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   20    *
   21    * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
   22    * or visit www.oracle.com if you need additional information or have any
   23    * questions.
   24    */
package com.clkj.nangang.util.encoder;

 import java.io.OutputStream;
import java.io.PushbackInputStream;

  /**
    32    * This class implements a BASE64 Character decoder as specified in RFC1521.
    33    *
    34    * This RFC is part of the MIME specification which is published by the
    35    * Internet Engineering Task Force (IETF). Unlike some other encoding
    36    * schemes there is nothing in this encoding that tells the decoder
    37    * where a buffer starts or stops, so to use it you will need to isolate
    38    * your encoded data into a single chunk and then feed them this decoder.
    39    * The simplest way to do that is to read all of the encoded data into a
    40    * string and then use:
    41    * <pre>
    42    *      byte    mydata[];
    43    *      BASE64Decoder base64 = new BASE64Decoder();
    44    *
    45    *      mydata = base64.decodeBuffer(bufferString);
    46    * </pre>
    47    * This will decode the String in <i>bufferString</i> and give you an array
    48    * of bytes in the array <i>myData</i>.
    49    *
    50    * On errors, this class throws a CEFormatException with the following detail
    51    * strings:
    52    * <pre>
    53    *    "BASE64Decoder: Not enough bytes for an atom."
    54    * </pre>
    55    *
    56    * @author      Chuck McManis
    57    * @see         CharacterEncoder
    58    * @see         BASE64Decoder
    59    */

   public class BASE64Decoder extends CharacterDecoder {

 /** This class has 4 bytes per atom */
  protected int bytesPerAtom() {
       return (4);
     }

     /** Any multiple of 4 will do, 72 might be common */
   protected int bytesPerLine() {
       return (72);
     }

    /**
    74        * This character array provides the character to value map
    75        * based on RFC1521.
    76        */
       private final static char pem_array[] = {
          //       0   1   2   3   4   5   6   7
                     'A','B','C','D','E','F','G','H', // 0
                   'I','J','K','L','M','N','O','P', // 1
                 'Q','R','S','T','U','V','W','X', // 2
                  'Y','Z','a','b','c','d','e','f', // 3
                 'g','h','i','j','k','l','m','n', // 4
                'o','p','q','r','s','t','u','v', // 5
                   'w','x','y','z','0','1','2','3', // 6
                 '4','5','6','7','8','9','+','/'  // 7
         };

     private final static byte pem_convert_array[] = new byte[256];

     static {
      for (int i = 0; i < 255; i++) {
           pem_convert_array[i] = -1;
       }
        for (int i = 0; i < pem_array.length; i++) {
           pem_convert_array[pem_array[i]] = (byte) i;
      }
      }
    byte decode_buffer[] = new byte[4];
    /**
   103        * Decode one BASE64 atom into 1, 2, or 3 bytes of data.
   104        */
   protected void decodeAtom(PushbackInputStream inStream, OutputStream outStream, int rem)
      throws java.io.IOException
    {
         int     i;
       byte    a = -1, b = -1, c = -1, d = -1;

      if (rem < 2) {
            throw new CEFormatException("BASE64Decoder: Not enough bytes for an atom.");
        }
         do {
           i = inStream.read();
            if (i == -1) {
               throw new CEStreamExhausted();
               }
         } while (i == '\n' || i == '\r');
         decode_buffer[0] = (byte) i;

      i = readFully(inStream, decode_buffer, 1, rem-1);
      if (i == -1) {
        throw new CEStreamExhausted();
       }

         if (rem > 3 && decode_buffer[3] == '=') {
             rem = 3;
          }
         if (rem > 2 && decode_buffer[2] == '=') {
             rem = 2;
        }
       switch (rem) {
        case 4:
           d = pem_convert_array[decode_buffer[3] & 0xff];
          // NOBREAK
       case 3:
            c = pem_convert_array[decode_buffer[2] & 0xff];
        // NOBREAK
     case 2:
         b = pem_convert_array[decode_buffer[1] & 0xff];
        a = pem_convert_array[decode_buffer[0] & 0xff];
             break;
        }

        switch (rem) {
         case 2:
           outStream.write( (byte)(((a << 2) & 0xfc) | ((b >>> 4) & 3)) );
           break;
       case 3:
              outStream.write( (byte) (((a << 2) & 0xfc) | ((b >>> 4) & 3)) );
             outStream.write( (byte) (((b << 4) & 0xf0) | ((c >>> 2) & 0xf)) );
             break;
         case 4:
            outStream.write( (byte) (((a << 2) & 0xfc) | ((b >>> 4) & 3)) );
             outStream.write( (byte) (((b << 4) & 0xf0) | ((c >>> 2) & 0xf)) );
          outStream.write( (byte) (((c << 6) & 0xc0) | (d  & 0x3f)) );
        break;
  }
       return;
    }
  }